Lambda, defined to be the air/fuel ratio divided by the stoichiometric air/fuel ratio, is an important parameter to control on a gaseous fueled internal combustion engine for meeting performance and exhaust gas emissions requirements.
Increasingly stringent exhaust gas emissions requirements have led to the introduction of electronics on spark ignited natural gas engines used in industrial applications. An electronic control module (ECM) based engine control system has been introduced on these products to perform the function of closed loop lambda control on the basis of feedback from an exhaust gas oxygen (EGO) sensor mounted in the exhaust stack.
To adjust lambda, an ECM controlled electrically actuated butterfly type fuel control valve has been introduced into the fuel flow path downstream of the pressure regulator and upstream of the carburetor. The system is such that all fuel admitted to the engine passes through this valve. The introduction of the fuel control valve in this manner introduced engine performance issues. The large volume that exists between the fuel control valve and the EGO sensor introduces significant dynamics into the lambda control loop. As a result, the closed loop lambda control was not able to be tuned aggressively, the fuel control valve position did not change quickly, and engine responsiveness suffered. The engine no longer responded adequately to speed/load transients.
Accordingly, what is desired is a system and method that addresses the above-identified issues. The system and method should be cost effective and easily adaptable to existing engines. The present invention addresses such a need.